A process of manufacturing a semiconductor device formed from the micropattern of an LSI, a VLSI, or the like, adopts a reduction projection exposure apparatus, which reduces a pattern formed on a mask, and projects and transfers it onto a substrate coated with a photosensitive agent. As the degree of integration of a semiconductor device increases, further micropatterning is required. The exposure apparatus has coped with micropatterning at the same time as the development of the resist process.
As a means for increasing the resolution of the exposure apparatus, there are a method of shortening the exposure wavelength and a method of increasing the numerical aperture of the projection optical system. In the latter case, there is proposed an immersion type exposure apparatus which implements a numerical aperture equal to the refractive index (1 or more) of a liquid by interposing a liquid layer between the final plane of the projection optical system and the surface of a substrate (e.g., wafer) to be exposed. As a conventional immersion type exposure apparatus, for example, Japanese Patent Laid-Open No. 6-124873 discloses an immersion type exposure apparatus comprising a wafer conveyance means and liquid bath. Japanese Patent Laid-Open No. 6-168866 discloses a system which sets a wafer in an immersion cassette and conveys the cassette.
FIG. 1 is a view showing the schematic structure of a conventional immersion type exposure apparatus. In FIG. 1, reference numeral 101 denotes an illumination system unit, which incorporates an exposure light source for emitting exposure light. Reference numeral 102 denotes a reticle stage, which supports a reticle serving as an exposure pattern master. Reference numeral 103 denotes a reduction projection lens, which reduces the exposure pattern of a master at a predetermined reduction exposure magnification ratio and projects the exposure pattern onto a substrate (wafer). Reference numeral 104 denotes an exposure apparatus main body, which supports the reticle stage 102, reduction projection lens 103, and the like.
Reference numeral 105 denotes an exposure stage which conveys a wafer chuck 105C which holds a wafer in the X and Y directions and positions the wafer chuck 105C on an exposure stage base 105B.
Reference numeral 106 denotes an alignment scope (microscope) which measures an alignment mark on the wafer and an alignment reference mark on the wafer chuck 105C, and measures alignment of the wafer held by the wafer chuck 105C. Reference numeral 107 denotes a focus scope which measures the planar shape of the wafer and the focus along the optical axis. After the end of alignment measurement and focus measurement, the exposure stage 105 moves to a predetermined immersion position on the exposure stage base 105B, and positions the wafer chuck 105C.
Reference numeral 113 denotes a wafer conveyance robot which supplies a wafer onto the wafer chuck 105C on the wafer stage 105 (wafer loading), and recovers the exposed wafer from the wafer chuck 105C (wafer unloading).
Reference numeral 114 denotes an immersion liquid tank which stores an immersion liquid. Before an exposure process, an immersion liquid drop recovery unit 115 drops the immersion liquid onto the wafer chuck 105C positioned by the exposure stage 105. After the exposure process, the immersion liquid drop recovery unit 115 recovers the immersion liquid from the wafer chuck 105C.
FIG. 2 is a flowchart for explaining the process flow of the exposure apparatus in FIG. 1. A wafer is loaded into an exposure area for performing exposure (S21), and then alignment measurement and focus measurement are executed (S22). After the end of measurement in step S22, the exposure stage 105 is moved and positioned at an immersion position at which the wafer chuck 105C on the stage receives the drops of a predetermined immersion liquid. Upon the completion of alignment, the immersion liquid drop recovery unit 115 drops the immersion liquid (S23).
Upon the completion of dropping the immersion liquid, the exposure stage 105 moves to an exposure position. Upon the completion of moving the exposure stage, the exposure apparatus starts an exposure process (S24).
After the end of the exposure process, the exposure stage 105 moves to a position for discharging the wafer in order to discharge (unload) the exposed wafer. Upon the completion of moving the exposure stage 105, the wafer conveyance robot 113 grips the wafer held on the wafer chuck 105C, and discharges (unloads) the wafer from the exposure area (S25). After the end of unloading (S25), the immersion liquid in the wafer chuck 105C is recovered by the immersion liquid drop recovery unit 115, and the wafer is dried (S26).
As described above, in the arrangement of the conventional immersion type exposure apparatus, a series of operations associated with the processes in steps S21 to S26 are serially performed. The time taken to process one wafer within the exposure area is the sum of processing times in steps S21 to S25, as shown in FIG. 3.
However, the conventional immersion type exposure apparatus serially executes a series of processes: wafer loading, alignment measurement/focus measurement, movement to an immersion position and dropping of an immersion liquid, an exposure process, wafer unloading, recovery of the immersion liquid, and a drying operation. The throughput (productivity) of the exposure apparatus is lower than that of a general exposure apparatus using no immersion method.